Method of regenerating pressing molds and method of manufacturing optical elements

ABSTRACT

Disclosed is a method of regenerating a pressing mold comprising removal of a carbon-based film from a pressing mold having the film on a molding surface thereof. The removal of the film is performed by etching with plasma of a hydrogen-based gas or treatment with UV ozone. Disclosed is a method of manufacturing an optical glass element comprising press molding of a heat-softened glass material in a pressing mold having a carbon-based film on a molding surface thereof. The pressing mold is that has been regenerated by removing a carbon-based film on the pressing mold having the film on the molding surface thereof by hydrogen gas plasma etching or UV ozone treatment, after which a carbon-based film has been formed on the molding surfaces from which the film has been removed. Provide is a method of regeneration that removes the carbon-based film on the molding surface of the base material of a pressing mold without damaging the surface of the base material of the pressing mold and that can reliably remove carbon-based films at reduced cost and in less time. Provide is a method of manufacturing optical glass elements employing a pressing mold that has been regenerated by this method.

TECHNICAL FIELD

[0001] The present invention relates to a method of regeneratingpressing molds suited to the removal and regeneration of deterioratedfilms on the molding surface of optical element pressing molds employedin the manufacturing of glass optical elements such as lenses and prismsby the press molding of glass materials, and to a method ofmanufacturing optical glass elements employing a pressing mold that hasbeen regenerated by the method of regenerating pressing molds.

BACKGROUND ART

[0002] It is known that a carbon-based film as a mold separation film isprovided on the molding surfaces of a pressing mold for optical glasselements.

[0003] This mold separation film is extremely useful because, as theglass comes into close contact with molding surfaces at high temperatureduring pressing, the mold separation film prevents fusion, maintains amirror surface on precision-processed molding surfaces, and maintainssliding properties between the molding surface and the glass when theglass is extended at high temperature. Carbon-based mold separationfilms in particular afford the advantages of low cost and goodperformance.

[0004] However, when a large number of pressing cycles is conducted, themold separation film partially separates, is lost, or the like, becomingworn down and no longer adequately performing its function. Whenpressing is continued still further, the glass fuses to the moldingsurfaces, reacts with the base material of the mold, and damages themold. Expensive molds in which the special base material of the mold hasbeen precisely processed to form the molding surface are employed. Whenthe above-described damage is imparted, the mold can no longer be used.Accordingly, the performance of the mold separation film must becontinuously checked. To repair deterioration of this film, it isnecessary to conduct a regeneration operation by removing the film aftera prescribed number of pressing cycles following formation of the moldseparation film and forming a new film. This makes it possible to bothconstantly press mold optical elements with high surface precision andextend the service life of the base material of the mold.

[0005] As a conventional optical element forming mold regenerationmethod, Japanese Unexamined Patent Publication (KOKAI) Heisei No.2-38330 (Patent Reference 1) describes a method of regenerating pressingmolds in which, after eliminating by oxygen plasma ashing the hardcarbon film on a glass pressing mold having a hard carbon-film on itsmolding surface, an aqueous solution of hydrogen fluoride or a saltthereof is used to cleanse the molding surface of the pressing mold.Further, Japanese Unexamined Patent Publication (KOKAI) Heisei No.6-345447 (Patent Reference 2) describes a method of regeneratingpressing molds by which, following the elimination of the carbon-basedfilm of a glass pressing mold having a carbon-based film on its moldingsurfaces by reduced pressure plasma etching with a fluorine-based gas ora mixed gas of fluorine-based gas and oxygen, the residual adheredmatter remaining by diffusion of the components in the glass is removedby scrubbing with abrasive grains of minute diameter. Japanese PatentPublication No. 2505893 (Patent Reference 3) describes a method ofregenerating pressing molds in which a portion of the film is etchedwith a plasma of oxygen-containing gas, and before the base material ofthe mold is etched, it is switched to etching with argon gas plasma toremove the film.

[0006] As stated in Patent Reference 1, when a hard carbon film isremoved by oxygen plasma ashing alone, the surface of the base materialis eroded by the oxygen plasma and a modified layer in the form of anoxide layer is formed on the surface of the base material. When acarbon-based film is formed on such the surface, the carbon-based filmadheres only weakly to the surface of the base material. And duringpress molding thereafter, there are problems such as separation of thecarbon-based coating. Accordingly, a method of cleansing the moldingsurface of the pressing mold with an aqueous solution of hydrogenfluoride or a salt thereof is described. This cleansing treatment iscapable of removing the modified layer on the surface of the basematerial. However, this removal slightly roughens the surface of thebase material. With repeated regeneration of the pressing mold, thissurface roughening accumulates. It is transferred during pressing,resulting in problems in the form of a defective external appearance inthe form of clouding and fogging due to optical scattering resultingfrom the roughness of the surface of the press molded product.

[0007] Patent Reference 2 describes a scrubbing method employing adiamond paste with an average particle diameter of 0.5 μm followingplasma etching. However, in this method, an oxide layer and a fluoridelayer are produced on the surface of the base material. Even whenscrubbing removes the volatile components of the glass remaining on themolding surface, it is impossible to remove the modified layer such asthe oxide layer and fluoride layer and roughness on the surface of thebase material since the base material is hard.

[0008] In the method described in Patent Reference 3, to prevent erosionof the surface of the base material by plasma, before etching the basematerial of the mold, a switch is made from ashing or etching by oxygengas plasma to ashing or etching by argon gas plasma to remove the film.However, this method requires judgment of when to make the switch.Determining when to make the switch requires additional equipment andsteps such as etching while monitoring the intensity of light emitted bythe etching compound by plasma light-emission analysis, thus increasingcost. Further, the cost of etching is doubled by using two plasmas, oneof oxygen gas and the other of argon gas.

[0009] As set forth above, conventional methods do not regenerateoptical element pressing molds with good precision and economy.

[0010] Accordingly, the object of the present invention is to provide amethod of regeneration that removes the carbon-based film on the moldingsurface of the base material of a pressing mold without damaging thesurface of the base material of the pressing mold and that can reliablyremove carbon-based films at reduced cost and in less time.

[0011] The present invention further provides a method of manufacturingoptical glass elements employing a pressing mold that has beenregenerated by this method.

DISCLOSURE OF THE INVENTION

[0012] To solve the above-described problems, the present invention is amethod of regenerating pressing molds comprising the removal of acarbon-based film from a pressing mold having the film on the moldingsurface thereof, characterized in that the removal of the film isperformed by etching with the plasma of a hydrogen-based gas ortreatment with UV ozone.

[0013] In the present invention, it is desirable for (1) thehydrogen-based gas to be hydrogen gas or a mixed gas of hydrogen gas andargon gas; (2) the pressing mold having a carbon-based film on themolding surface thereof to be heated to greater than or equal to 100° C.and less than or equal to 600° C. during the UV ozone treatment; (3) themolding surfaces to be cleansed with an acid solution or an alkalisolution prior to conducting plasma etching or UV ozone treatment; (4) afurther step of forming a carbon-based film on the molding surface fromwhich the film has been removed to be included; and (5) the pressingmold that is subjected to the etching or UV ozone treatment to have adeteriorated film.

[0014] The present invention further relates to a method ofmanufacturing optical glass elements comprising the press molding of aheat-softened glass material in a pressing mold having a carbon-basedfilm on the molding surface thereof, characterized in that the pressingmold has been regenerated by removing by hydrogen-based gas plasmaetching or UV ozone treatment of a carbon-based film on the pressingmold having the film on the molding surface thereof, after which acarbon-based film has been formed on the molding surfaces from which thefilm has been removed.

[0015] In the present invention, the carbon-based film of the pressingmold that is subjected to etching or UV ozone treatment has desirablydeteriorated.

BRIEF DESCRIPTION OF THE FIGURES

[0016]FIG. 1 is a descriptive drawing of a pressing mold with acarbon-based film formed on the molding surfaces thereof.

[0017]FIG. 2 is a descriptive drawing of a plasma processing device.

[0018]FIG. 3 is a descriptive drawing of a UV ozone treatment device.

BEST MODE OF IMPLEMENTING THE INVENTION

[0019] The present invention is a method of regenerating pressing moldscomprising the step of removing a carbon-based film from a pressing moldhaving the film on the molding surfaces thereof.

[0020] The pressing mold that is regenerated by the method of thepresent invention has a carbon-based film on the molding surfacethereof. The material employed as the base material of the mold isselected on the basis of the possibility of processing into an opticalmirror surface, whether it has mechanical strength capable ofwithstanding press impact, and the like.

[0021] Examples of materials that can be selected from such perspectivesare SiC, WC, TiC, TaC, BN, TiN, AlN, Si₃N₄, SiO₂, Al₂O₃, ZrO₂, W, Ta,Mo, cermet, syalon, mullite, carbon composite (C/C), carbon fiber (CF),WC—Co alloy, stainless steel, and the like. In particular, pressingmolds having a mold base material in the form of SiC, WC, TiC, TaC,WC—Co alloy, and stainless steel are highly reactive with oxygen andfluorine and have surfaces that tend to be modified or damaged by theetching of conventional methods employing oxygen and fluorine. However,since the selection ratio stated further below works advantageously whenthe present invention is applied, marked results by the presentinvention are achieved.

[0022] In the course of precision processing of the molding surface, theroughness of the molding surface is desirably less than or equal to 80nm, preferably less than or equal to 50 nm, as an Rmax evaluated bymeasurement with atomic force microscopy (AFM).

[0023] Carbon-based films applied to the molding surfaces are filmscomprising carbon as primary component and examples are diamond-likecarbon films (DLC films hereinafter), hydrogenerated diamond-like carbonfilms (DLC:H hereinafter), tetrahedral amorphous carbon films (ta-Chereinafter), hydrogenerated tetrahedral amorphous carbon films (ta-C:Hhereinafter), amorphous carbon films (a-C hereinafter), andhydrogenerated amorphous carbon films (a-C:H hereinafter). However, thepresent invention is not limited to these carbon-based films.

[0024] Laminates of two or more of these films and composite films(where multiple film forming methods are applied simultaneously) mayalso be employed. These carbon-based films function to enhance the moldseparability of the molding surfaces.

[0025] [Etching with the Plasma of a Hydrogen-Based Gas]

[0026] In the first aspect of the method of regenerating pressing moldsof the present invention, the film on the pressing mold is removed byetching with the plasma of a hydrogen-based gas.

[0027] Etching with the plasma of a hydrogen-based gas affords theadvantage of removing the carbon-based film without damaging the surfaceof the base material.

[0028] Here, the term “hydrogen-based gas” refers to a gas containinghydrogen, desirably a gas containing greater than or equal to 1 vol % ofhydrogen, preferably a gas containing greater than or equal to 3 vol %of hydrogen. More specifically, hydrogen gas or a mixed gas of hydrogengas and argon gas is employed as the hydrogen-based gas. The mixed gaswith argon gas desirably contain greater than or equal to 1 vol % ofhydrogen gas, preferably greater than or equal to 3 vol % of hydrogen.

[0029] The term “etching” refers to a method of removing the surfacelayer by means of a chemical reaction and includes ashing. The term“plasma” is a state in which charged particles produced by ionizationare present in a gas, and includes mixed gases of ions and radicals andgases comprised chiefly of ions and radicals.

[0030] Etching by hydrogen-based gas plasma can be conducted with aknown device by a method such as reactive ion etching or direct plasma.Such devices can be obtained in the form of commercial products. Theetching conditions are suitably selected based on the device employed.The standard condition is a plasma output of 100 to 2,000 W. When theplasma output is either too high or too low, the plasma sometimes doesnot stabilize. The base plate temperature can be made from roomtemperature to 300° C.; when excessively high, the selection ratiodescribed further below decreases, and when excessively low, the etchingrate tends to drop. When ordinary pressure is employed in an ordinarypressure plasma processing device and when a gas pressure of about from1 Pa to 100 KPa is employed in a reduced-pressure plasma processingdevice, stable plasma can be generated.

[0031] The etching with the plasma of a hydrogen-based gas that isemployed in the present invention is characterized by high selectivityof the substance to be etched. Generally, the ratio of the etching rateof the film to that of the base material is called the selection ratio.Hydrogen has an etching rate for carbon that is comparable to that ofthe oxygen and CF₄ employed in conventional art, but has a quite lowetching rate for the base material of the mold. For example, when themold base material is SiC or WC, the etching rate by the plasma of ahydrogen-based gas is about {fraction (1/100)}^(th) that when a plasmaof oxygen or CF₄ is employed. This is because of the low reactivity ofhydrogen plasma with the mold base material; any reaction layergenerated by the mold base material and hydrogen is extremely thin.

[0032] Accordingly, the use of hydrogen-based gas is characterized by anincrease in the selection ratio so that even when etching processing isconducted in a manner exceeding what is necessary to completely removethe film, the surface of the base material remains essentiallyunmodified. That is, once the carbon-based film has been removed byetching, the mold base material is not etched even when thehydrogen-based plasma comes in contact with the base material of themold. Thus, even when the etching period is longer than necessary, thereis an advantage in that the base material is not modified or damaged.Further, in the event that a reaction layer is produced on the surfaceof the base material, it is a hydrogen-modified layer and does notimpede adhesion of the film when forming a new carbon-based film duringregeneration.

[0033] [UV Ozone Treatment]

[0034] In the second aspect of the method of regenerating pressing moldsof the present invention, the film on the pressing mold is removed by UVozone treatment.

[0035] The term “UV ozone treatment” refers to a method of generatingozone with ultraviolet radiation and rapidly decomposing and volatizingorganic contaminants through the oxidizing power of excited oxygen atomsgenerated by the decomposition of this ozone. This method is employed inultraprecise cleansing, sterilization, and deodorizing. The oxidizingpower of excited oxygen atoms is less than that of oxygen plasma; thecarbon etching rate is about ½ to ⅛. The etching rate on the mold basematerial is less than or equal to {fraction (1/100)}. For example, whenSiC or WC is employed as the mold base material and UV ozone treatmentis conducted, the selection ratio (the etching rate on carbon-basedfilm/the etching rate on mold base material) is about ten-fold that ofthe selection ratio of oxygen plasma and CF₄ plasma. This is because theoxidizing power of excited oxygen atoms on the mold base material in UVozone treatment is low and the reaction layer with the mold basematerial, when one is generated, is extremely thin.

[0036] Since the thickness of the reaction layer is extremely thin (forexample, the film thickness can be kept to less than or equal to 1 nm),there is no decrease in adhesion when reforming the carbon-based film.Further, since no chemicals are employed, little burden is placed on theenvironment. The power of the UV light source employed to generate UVozone is desirably greater than or equal to 100 W, preferably greaterthan or equal to 200 W. Further, oxygen is necessary in the atmosphere.The oxygen concentration is desirably greater than or equal to 5 vol %,preferably greater than or equal to 10 vol %. The UV ozone treatmentgenerally lasts for several minutes to several hours. The UV ozonetreatment (the ultraviolet radiation ozone process) can be conductedwith a known device.

[0037] To accelerate the decomposition and removal of the carbon-basedfilm by UV ozone treatment in the method of the present invention, it isdesirable to heat the base plate. However, when heating exceeds 600° C.,with some base plates, the surface of the pressing mold is oxidized, theadhesive strength of the mold separation film during the formation ofthe new mold separation film is compromised, and regeneration of themold separation film is sometimes prevented. Accordingly, the base plateis desirably heated to less than 600° C. during UV ozone treatment.Further, the base plate is preferably heated to less than or equal to400° C. during UV ozone treatment. When the base plate is heated to atemperature of less than 100° C., the rate of decomposition and removalof the carbon-based film slows during UV ozone treatment, so heating ofthe base plate to greater than or equal to 100° C. in UV ozone treatmentis desirable. It is unnecessary for the base plate temperature to befixed; it is possible to vary the temperature by setting the base platetemperature high at the start of the UV ozone treatment and subsequentlygradually lowering it.

[0038] The UV ozone treatment in the present invention affords the sameadvantage as etching by hydrogen-based gas plasma of high selectivity ofthe substance that is etched. That is, once the carbon-based film on thepressing mold has been removed, the base material of the pressing moldis not modified or damaged.

[0039] Trace amounts of glass or volatile components of glass and thelike sometimes adhere to and remain on the carbon-based film on themolding surfaces of the pressing mold after continuous pressing. Amongthese, there are materials that tend not to be removed by hydrogen-basedplasma etching or UV ozone treatment. Accordingly, in the presentinvention, the carbon-based film of the molding surface of the pressingmold is desirably cleansed in advance with an acid or alkali solution toremove material adhering to the surface.

[0040] Examples of acid solutions are 1 to 50 wt % concentrations ofhydrofluoric acid, acid ammonium fluoride aqueous solutions, nitricacid, sulfuric acid, hydrochloric acid, and a mixture of nitric acid andsulfuric acid. Examples of alkali solutions are 5 to 70 wt %concentrations of sodium hydroxide aqueous solutions, potassiumhydroxide aqueous solutions, and lithium hydroxide aqueous solutions.The period of immersion in the acid solution or alkali solution is fromseveral minutes to several hours, and the temperature of the immersionsolution is desirably from room temperature to around 50° C.

[0041] The method of regeneration of the present invention furthercomprises the formation of a carbon-based film on the surface of thebase material from which the film has been removed.

[0042] The carbon-based film is the above-described carbon film. Whenforming the film, for example, diamond films can be formed by microwaveplasma CVD, the hot filament method, the plasma jet method, electroncyclotron resonance plasma CVD, DC-plasma CVD, optical CVD, laser CVDand the like. DLC films and DLC:H films can be formed by microwaveplasma CVD, hot filament CVD, the plasma jet method, electron cyclotronresonance plasma CVD, DC-plasma CVD, optical CVD, laser CVD, theion-plating method and other ionization vapor deposition methods,sputtering, and the like. ta-C films and ta-C:H films can be formed byFCA (Filtered Cathodic Arc). a-C and a-C:H films can be formed by plasmaCVD, ion-plating methods and other ionization vapor deposition methods,sputtering, and vapor deposition methods.

[0043] The thickness of the carbon-based film is desirably about from 1nm to μm, preferably from 2 nm to 100 nm. When the film is too thin, anadequate mold separation property and durability cannot be achieved.When the film is too thick, there is a problem in that adhesion to themold base material decreases.

[0044] In the regeneration method of the present invention, the pressingmold subjected to the etching or UV ozone treatment may have adeteriorated film. This regeneration method is also applicable topressing molds having other films.

[0045] The regeneration method of the present invention is not limitedto pressing molds employed for optical elements such as lenses, mirrors,gratings, and prisms, but can also be applied to pressing molds used formolded articles of glass and plastic that are not optical elements.

[0046] [Method of Manufacturing Optical Glass Elements]

[0047] The present invention includes a method of manufacturing opticalglass elements comprising the step of press molding a heat-softenedglass material in a pressing mold having a carbon-based film on themolding surface thereof. This method of manufacturing optical glasselements is characterized in that the pressing mold has been regeneratedby removing a carbon-based film on a pressing mold having the film onthe pressing surface thereof by etching with a hydrogen-based gas plasmaor by UV ozone treatment, and then forming a carbon-based film on themolding surface from which the film has been removed. The method ofremoving the carbon-based film is identical to that described under theregeneration method of the present invention set forth above. Further,the carbon-based film is formed on the molding surface from which a filmhas been removed. The carbon-based film can also be formed by the samemethods as described for the regeneration method of the presentinvention. Further, press molding of the heat-softened glass materialcan be conducted by known methods.

[0048] Neither the glass material nor the shape of the glass materialthat is press molded by a pressing mold applying the present inventionis specifically limited. However, the effect of the present invention ismarked in glass materials with which deterioration of the moldseparation film tends to occur, that is, in glass materials requiringfrequent regeneration of the mold separation film. For example, sincewater molecules tend to be picked up by the glass components of glassmaterials comprised of phosphate-based optical glass, reactivity withthe mold separation film on the molding surface is high anddeterioration of the mold separation film is rapid. Accordingly,frequent regeneration of the mold separation film becomes necessary andthe effect of the present application is marked. Similarly, examples ofhighly reactive glasses are fluorophosphate-based and borate-basedoptical glasses.

[0049] Further, to suppress the reactivity of the above-mentioned highlyreactive glasses, the glass material temperature is sometimes set lowduring pressing (for example, set to a temperature corresponding to aglass viscosity of 10 ^(7.5) to 10^(8.5) dPa·s). In such cases, thenecessary thickness cannot be achieved without increasing the pressingload. The pressing load is usually about 30 to 300 kg/cm². However, forthe above-mentioned highly reactive glass materials, a high load area(for example, from about 200 to 250 kg/cm²) is suitably applied withinthis range. However, the mold separation film is rapidly damaged bypressing in the high load area and the frequency of regeneration ishigh. Thus, the present invention is extremely advantageous for theregeneration of pressing molds employed in the pressing of glasses ofhigh reactivity.

[0050] Further, for items with shapes tending to crack when the opticalelement is formed (such as biconvex lenses, biconcave lenses, andmeniscus lenses in which the difference between the center thickness andthe edge thickness of the lens is greater than or equal to 2) thethickness of the mold separation film is generally increased to preventcracking. For example, the thickness of the mold separation film is setto about 30 to 100 nm. When such a mold separation film deteriorates, itis extremely important to efficiently and completely remove the moldseparation film without damaging the base material. Thus, theapplication of the present invention to the regeneration of pressingmolds having thick mold separation films is also extremely effective.

[0051] Further, even slight surface roughness of the mold separationfilm is not permitted in optical elements imposing strict surfaceroughness requirements on the molding surface, such as an Rmax of 20 nmor less. Thus, it is quite important to increase the frequency ofregeneration of the mold separation film without causing deteriorationof the mirror surface of the base material of the mold; the presentinvention is also efficiently applied in such cases.

[0052] In the press molding step, a glass material that has been heatsoftened to achieve a glass viscosity of less than or equal to 10⁹ dPa·sis press molded in a pressing mold. At that time, the glass material isfed into the interior of the pressing mold and the mold and glassmaterial are both heated to the above-mentioned temperature prior tomolding, after which press molding may be conducted (referred to asisothermal pressing). It is also acceptable to feed a glass materialthat has been heat softened outside the mold into the pressing mold andimmediately conduct press molding. In the latter case, the temperatureof the glass material can be set higher than the mold temperature(referred to as anisothermal pressing), thereby making it possible toset the temperature of the mold lower than in isothermal pressing. Forexample, it is possible to heat the glass material to a temperaturecorresponding to a glass viscosity of greater than or equal to 10⁶ andless than 10⁸ dPa·s. Further, the pressing mold may be heated to atemperature corresponding to a glass viscosity of greater than or equalto 10⁸ and less than 10¹¹ dPa·s. This method inhibits deterioration ofthe mold separation film, is advantageous to extending the service lifeof the base material of the mold, and reduces the time required for themold heating cycle, improving productivity. In both of these pressingmethods, the glass material following pressing is cooled to atemperature less than or equal to the transition point temperature whilestill in the mold, and then taken out from the mold.

[0053] The present invention as set forth above provides a method ofquickly and inexpensively regenerating pressing molds yielding highprecision molded articles by removing the film by hydrogen-based gasplasma etching or UV ozone treatment even when a carbon-based film ofthe pressing mold has been damaged by forming optical elements with apressing mold the molding surfaces of which have been coated with thefilm.

EXAMPLES

[0054] The present invention is described in detail below throughExamples.

Example 1

[0055]FIG. 1 shows an embodiment of an optical element pressing moldrelating to the present invention. In FIG. 1, 1 denotes the basematerial of the mold and 2 denotes the carbon film (mold separationfilm) provided on the molding surfaces that mold the glass material.

[0056] The optical element pressing mold will be described in detailfirst. A mirror-surface mold base material with polycrystallized SiCmolding surfaces formed by CVD that had been polished to Rmax=18 nm wasemployed (the roughness was measured by AFM). This mold was thoroughlycleansed, after which a DLC:H film was formed on the molding surfacewith an ion-plating film-forming device. Depth analysis by ESCA revealedthe thickness of the DLC:H film to be 80 nm. Microscopic Raman analysisrevealed two peaks near 1,380 cm⁻¹ (D-band) and near 1,580 cm⁻¹ (G-band)based on the medium-range order of disordered clusters and graphiteclusters. The film structure was confirmed to be a DLC structure.

[0057] A spherical glass material (preform) of glass A (transitiontemperature Tg=500° C., yield point Ts=540° C.) of optical bariumborosilicate glass adjusted to prescribed weight was placed in thecavity of a pressing mold and the pressing mold was positioned within apressing device. Heating was conducted to 620° C. in a nitrogen gasatmosphere and pressure of 150 kg/cm² was applied for 1 min. Followingthe release of pressure, cooling was conducted at a rate of −50° C./minto 480° C., after which cooling was conducted at a rate of −100° C./minor greater. When the temperature of the press molded product had droppedto 200° C. or below, the molded product was retrieved. In this manner, abiconvex lens with an outer diameter of 12 mm φ, a center thickness of1.5 mm, and an edge thickness of 0.5 mm was molded. In continuousmolding, optical elements in the form of good molded products wereobtained.

[0058] The molding surface was observed by optical microscopy after1,000 molding cycles had been performed, revealing trace fusion adhesionof volatile material. Accordingly, immersion was conducted for 30 min ina 20% acid ammonium fluoride aqueous solution at room temperature.Following cleansing, the molding surfaces were observed by opticalmicroscopy, revealing no trace fusion or adhesion of volatile matter andconfirming removal by acid cleansing.

[0059] Next, the acid-cleansed optical element pressing mold was placedon the base plate in the chamber of a plasma processing unit such as isshown in FIG. 2. The interior of the chamber was evacuated to a vacuumof 5 Pa, and while introducing a mixed gas of 3.5% hydrogen and 96.5%argon into the chamber to 100 Pa, electricity was discharged to generatea plasma. Etching by hydrogen-based plasma was conducted for 20 min.Following etching, the molding surfaces were observed by opticalmicroscopy and scanning electron microscopy (SEM), revealing no residue.The DLC:H film had been completely removed. Measurement of roughness byatomic force microscopy (AFM) revealed an Rmax of 19 nm. The surfaceprofile of the base material molding surface had been preserved.

[0060] After thoroughly cleansing the optical element pressing moldfollowing this treatment, an ion plating film-forming device wasemployed to form a DLC:H film to a thickness of 80 nm on the moldingsurface. There was neither roughness nor gaps in the DLC:H film, andduring continuous molding, optical elements were again obtained in theform of good molded products.

[0061] This process of 1,000 cycles of molding followed by regenerationprocessing consisting of acid cleansing, etching by hydrogen-basedplasma, and DLC:H film formation was repeated 100 times. However, therewas little actual surface deterioration of the molding surfaces of thepressing mold or decrease in ability to form a DLC:H film, and noproblems with the quality of external appearance, such as clouding ofthe molded product, were encountered. The surface roughness of themolding surfaces following 100 cycles of regeneration processing was anRmax (measured by AFM) of 30 nm.

Comparative Example 1

[0062] Instead of etching the optical element pressing mold with ahydrogen-based gas plasma following 1,000 cycles of molding in Example1, etching was conducted with oxygen gas plasma. As in Example 1, theacid-cleansed optical element pressing mold was placed on the base platein the chamber of a plasma processing device, the interior of thechamber was evacuated to a vacuum of 5 Pa, and while introducing oxygengas into the chamber to 5×10⁻³ Torr, electricity was discharged togenerate a plasma. Etching by oxygen gas plasma was then conducted for20 min. Observation of the molding surfaces by optical microscopy andSEM revealed no residue; the DLC:H film had been completely removed.

[0063] Further, after thoroughly cleansing the optical element pressingmold following this treatment, an ion-plating film-forming device wasemployed to form a DLC:H film to a thickness of 80 nm on the moldingsurfaces. When continuous molding of the same glass materials was begun,a defective external appearance such as clouding and fogging wasexhibited on the molding surfaces after 30 pressing cycles. Observationof the molding surfaces after molding revealed separation of the DLC:Hfilm.

Comparative Example 2

[0064] Instead of etching the optical element pressing mold with ahydrogen-based gas plasma following 1,000 cycles of molding as inExample 1, etching was conducted with argon gas plasma. As in Example 1,the acid-cleansed optical element pressing mold was placed on the baseplate in the chamber of a plasma processing device, the interior of thechamber was evacuated to a vacuum of 5 Pa, and while introducing argongas into the chamber to 100 Pa, electricity was discharged to generate aplasma. Etching by argon gas plasma was then conducted for 300 min.Observation of the molding surfaces by optical microscopy and SEMrevealed that the DLC:H film remained over the entirety of the moldingsurfaces.

[0065] Further, after thoroughly cleansing the pressing mold, anion-plating film-forming device was employed to form a DLC:H film to athickness of 80 nm on the molding surfaces. When continuous molding withthe same glass materials was begun, defective external appearance suchas clouding and fogging was exhibited by the molding surfaces afterabout 50 pressing cycles.

Examples 2 to 6

[0066] With the exceptions that the base material of the mold,carbon-based mold separation film, method of forming the mold separationfilm, thickness of the mold separation film, optical glass, pressingconditions, cleansing prior to plasma treatment, and gas employed inetching (plasma source) were varied as indicated in Tables 1 and 2,regeneration processing was repeated 100 times in the same manner as inExample 1. As indicated in the tables, the actual surface deteriorationon the molding surfaces of the pressing mold and decrease in the abilityto form the carbon-based mold separation film were quite small. Noproblems were found with the quality of the external appearance of themolded products.

[0067] The lenses molded in Examples 2 to 6 were as follows.

[0068] Example 2: Concave meniscus lens with an outer diameter of 10 mmφ, center thickness of 0.5 mm, and edge thickness of 1.5 mm.

[0069] Example 3: Biconcave lens with an outer diameter of 12 mm φ,center thickness of 0.6 mm, and edge thickness of 1.6 mm.

[0070] Example 4: Convex meniscus lens with an outer diameter of 15 mmφ, center thickness of 1.5 mm, and edge thickness of 0.6 mm.

[0071] Example 5: Concave meniscus lens with an outer diameter of 16 mmφ, center thickness of 0.8 mm, and edge thickness of 1.8 mm.

[0072] Example 6: Convex meniscus lens with an outer diameter of 22 mmφ, center thickness of 1.8 mm, and edge thickness of 0.4 mm. TABLE 1Item Example 1 Comp. Example 1 Example 2 Example 3 Mold base materialSiC SiC WC Stainless steel Carbon-based mold DLC:H DLC:H ta-C DLCseparation film Method of forming mold Ion plating Ion plating FCAmethod Sputtering separation film Optical glass (Tg/Ts) Glass A Glass AGlass B Glass C Barium borosilicate glass Barium borosilicate glassBorate glass (500° C./535° C.) Phosphate glass (500° C./540° C.) (500°C./540° C.) (365° C./403° C.) Pressing* conditions 620° C./1 min 620°C./1 min 600° C./2 min 450° C./2 min Cleansing process prior to 20% acidammonium 20% acid ammonium 10% KOH aqueous solution/ None plasmatreatment fluoride aqueous solution/30 min fluoride aqueous solution/30min 5 min immersion immersion immersion Plasma source gas Hydrogen gas3.5% Oxygen gas Hydrogen gas Hydrogen gas 3.5% Argon gas 96.5% Argon gas96.5% Results of regeneration ⊚ X ⊚ ◯ process***

[0073] TABLE 2 Item Example 4 Example 5 Example 6 Comp. Example 2 Moldbase material WC SiC Crystallized glass** SiC Carbon-based mold DLCFirst layer: DLC:H First layer: C DLC:H separation film Second layer:DLC Second layer DLC:H Method of forming mold Sputtering First layer:ion plating First layer: acetylene gas Ion plating separation filmSecond layer: sputtering thermal decomposition Second layer: ion platingOptical glass (Tg/Ts) Glass D Glass E Glass C Glass A Borate glass (520°C./ Borate glass (560° C./600° C.) Phosphate glass Barium borosilicateglass 560° C.) (365° C./403° C.) (500° C./540° C.) Pressing* conditions620° C./1 min 660° C./2 min 450° C./2 min 620° C./1 min Cleansingprocess prior to 5% acid ammonium 5% acid ammonium fluoride None 20%acid ammonium plasma treatment fluoride aqueous solution/ aqueoussolution/10 min fluoride aqueous solution/30 min 10 min immersionimmersion immersion Plasma source gas Hydrogen gas 5% Hydrogen gasHydrogen gas 3.5% Argon gas Argon gas 95% Argon gas 96.5% Results ofregeneration ◯ ⊚ ◯ X process***

Example 7

[0074] In Example 1, instead of etching the optical element pressingmold with hydrogen gas plasma after 1,000 pressing cycles, as shown inFIG. 3, the acid-cleansed optical element pressing mold was placed in aUV ozone treatment unit with a UV lamp having an output of 350 W, theinterior of the chamber was evacuated to a vacuum of 10 Pa, oxygen gaswas introduced until the interior of the chamber reached atmosphericpressure, the UV lamp was turned on, and UV ozone treatment wasconducted for 20 min.

[0075] Observation of the molding surfaces by optical microscopy and SEMrevealed no residue; the DLC:H film had been completely removed.Roughness measurement by AFM revealed an Rmax of 25 nm; the surfaceprofile of the base material surface had been preserved.

[0076] After thoroughly cleansing the optical element pressing moldfollowing this treatment, an ion plating mold-forming device wasemployed to form a DLC:H film to a thickness of 30 nm on the moldingsurface. There were no anomalies such as roughness or gaps in the DLC:Hfilm, and during continuous molding, optical elements were againobtained in the form of good molded products.

[0077] This process of 1,000 cycles of molding followed by regenerationprocessing consisting of acid cleansing, etching by hydrogen-basedplasma, and DLC:H film formation was repeated 100 times. However, therewas little actual surface deterioration of the molding surfaces of thepressing mold or decrease in ability to form a DLC:H film. No problemswith the quality of external appearance were encountered. The surfaceroughness of the molding surfaces following 100 cycles of regenerationprocessing was an Rmax (measured by AFM) of 31 nm.

Comparative Example 3

[0078] Instead of processing the optical element pressing mold with UVozone following 1,000 cycles of molding as in Example 7, heat processingwas conducted for 30 min at 800° C. in an oxygen atmosphere. Observationof the molding surfaces by optical microscopy, scanning electronmicroscopy (SEM), and atomic force microscopy (AFM) revealed no residue;the DLC:H film had been completely removed. However, measurement ofroughness by AFM revealed an Rmax of 128 nm; roughening of the basematerial molding surface had progressed.

[0079] Further, after thoroughly cleansing the pressing mold, anion-plating film-forming device was employed to form a DLC:H film to athickness of 30 nm on the molding surfaces. When continuous molding withthe same glass materials was begun, defective external appearance suchas clouding and fogging was exhibited by the molding surfaces in thefirst pressing cycle.

Examples 8 to 12

[0080] With the exceptions that the base material of the mold,carbon-based mold separation film, method of forming the mold separationfilm, thickness of the mold separation film, optical glass, pressingconditions, cleansing prior to UV ozone treatment, and use or lackthereof of UV treatment were varied as indicated in Tables 3 and 4,regeneration processing was repeated 100 times in the same manner as inExample 7. As indicated in the tables, the actual surface deteriorationon the molding surfaces of the pressing mold and decrease in the abilityto form a carbon-based mold separation film were quite small. Noproblems were found with the quality of the external appearance of themolded products.

[0081] The lenses molded in Examples 8 to 12 were as follows.

[0082] Example 8: Concave meniscus lens with an outer diameter of 12 mmφ, center thickness of 0.8 mm, and edge thickness of 1.9 mm.

[0083] Example 9: Biconcave lens with an outer diameter of 8 mm φ,center thickness of 0.4 mm, and edge thickness of 1.2 mm.

[0084] Example 10: Convex meniscus lens with an outer diameter of 18 mmφ, center thickness of 1.8 mm, and edge thickness of 0.6 mm.

[0085] Example 11: Concave meniscus lens with an outer diameter of 12 mmφ, center thickness of 0.4 mm, and edge thickness of 1.8 mm.

[0086] Example 12: Biconvex lens with an outer diameter of 6 mm φ,center thickness of 1.2 mm, and edge thickness of 0.4 mm. TABLE 3 ItemExample 7 Comparative Example 3 Example 8 Mold base material SiC SiCStainless steel Carbon-based mold DLC:H DLC:H DLC separation film Methodof forming mold Ion plating Ion plating Sputtering separation filmThickness of mold separation 30 nm 30 nm 20 nm film Optical glass(Tg/Ts) Glass A Glass A Glass C Barium borosilicate glass Bariumborosilicate glass Phosphate glass (500° C./540° C.) (500° C./540° C.)(365° C./403° C.) Pressing* conditions 620° C./1 min 620° C./1 min 450°C./2 min Cleansing process prior to 20% acid ammonium 20% acid ammoniumNone UV ozone treatment fluoride aqueous solution/30 min fluorideaqueous solution/30 min immersion immersion Use or absence of UV ozoneUsed 20 min in oxygen gas. Not used. 30 min in oxygen Used. Dried in airfor 15 min treatment gas. Base plate heating None 800° C. None Resultsof regeneration ◯ X ◯ process***

[0087] TABLE 4 Item Example 9 Example 10 Example 11 Example 12 Mold basematerial WC SiC SiC Crystallized glass*** Carbon-based mold ta-C Firstlayer: DLC:H First layer: DLC:H First layer: C separation film Secondlayer: DLC Second layer: ta-C Second layer: DLC:H Method of forming moldFiltered cathodic arc (FCA) First layer: ion plating First layer: ionplating First layer: acetylene gas separation film Second layer:sputtering Second layer: FCA thermal decomposition Second layer: ionplating Thickness of mold 80 nm 160 nm 120 nm 200 nm separation filmOptical glass (Tg/Ts) Glass D Glass E Glass B Glass C Borate glassBorate glass Borate glass Phosphate glass (520° C./560° C.) (560°C./600° C.) (500° C./535° C.) (365° C./403° C.) Pressing* conditions620° C./1 min 660° C./2 min 620° C./1 min 450° C./2 min Cleansingprocess prior to 5% acid ammonium fluoride 5% acid ammonium fluoride 20%acid ammonium None UV ozone treatment aqueous solution/10 min aqueoussolution/10 min fluoride aqueous solution/15 min immersion immersionimmersion UV ozone treatment 30 min in oxygen gas. 40 min in air 30 minin dry air 50 min in oxygen gas Base plate heating 400° C. None 300° C.300° C. Results of regeneration ⊚ ◯ ⊚ ◯ process***

1-8. (Canceled)
 9. A method of regenerating a pressing mold having amolding surface, said molding surface having a film containing carbonwhich is deteriorated by pressing, comprising: removing the deterioratedfilm by etching with plasma of a gas containing hydrogen; and forming afilm containing carbon on the molding surface.
 10. The method of claim 9wherein the gas contains hydrogen and argon.
 11. The method of claim 9further comprising cleansing the molding surface with a solution of anacid or an alkali prior to the removing of the film.
 12. A method ofregenerating a pressing mold having a molding surface, said moldingsurface having a film containing carbon which is deteriorated bypressing, comprising: removing the deteriorated film by a treatment withozone; and forming a film containing carbon on the molding surface. 13.The method of claim 12 wherein the ozone is generated by ultra-violetradiation.
 14. The method of claim 13 wherein the pressing mold isheated to 100° C. to 600° C. when the treatment is carried out.
 15. Themethod of claim 13 further comprising cleansing the molding surface witha solution of an acid or an alkali prior to the removing of the film.16. A method of manufacturing an optical glass element with a pressingmold, said pressing mold having a molding surface comprising a filmcontaining carbon, comprising: press molding a heat-softened glassmaterial with the pressing mold; cooling the press molded glass materialin the pressing mold; and taking out the press molded glass materialfrom the pressing mold, wherein the pressing mold is regenerated byremoving a film containing carbon by etching with plasma of a gascontaining hydrogen, and forming the film containing carbon on themolding surface.
 17. The method of claim 16 wherein the gas containshydrogen and argon.
 18. The method of claim 16 wherein the moldingsurface is cleansed with a solution of an acid or an alkali prior to theremoving of the film.
 19. A method of manufacturing an optical glasselement with a pressing mold, said pressing mold having a moldingsurface comprising a film containing carbon, comprising: press molding aheat-softened glass material with the pressing mold; cooling the pressmolded glass material in the pressing mold; and taking out the pressmolded glass material from the pressing mold, wherein the pressing moldis regenerated by removing a film containing carbon by a treatment withozone, and forming the film containing carbon on the molding surface.20. The method of claim 19 wherein the ozone is generated byultra-violet radiation.
 21. The method of claim 19 wherein the pressingmold is heated to 100° C. to 600° C. when the treatment is carried out.22. The method of claim 19 wherein the molding surface is cleansed witha solution of an acid or an alkali prior to the removing of the film.23. The method of claim 16 wherein the molding surface comprises asurface roughness of 20 nm or less in terms of Rmax.
 24. The method ofclaim 16 wherein the optical element comprising phosphate glass,fluorophosphate, or borate glass.